EXSC 329 Energy Systems and Energy Expenditure

What is true about the blending of energy systems?

the body is never using only one energy system, usage depends on rate of ATP production needed but always involves every system

What limits glycolysis?

acidosis and rate limiting enzymes that slow enzyme activity and inhibit calcium binding

What limits the ATP-PCr system?

small stores of easily accessibly substrate that cannot sustain long duration exercise

What is the crossover concept?

the point where there is a relative balance between carb and fat metabolism, where there is a 1:1 use of carbs to fats

Why do we switch to carb use at higher intensities?

carbs are broken down faster than fats

carbs are a more efficient use of O2 molecules

Type II (explosive) muscles are more glycolytic

increased catecholamines stimulate glycolytic enzymes

How does endurance training affect the crossover point?

greater endurance improves fat oxidation and increases oxidative enzymes and the number of mitochondria, allowing the crossover point to shift to a higher intensity

What is glycogen sparing?

when endurance training shifts the crossover point to a higher intensity, protecting glycogen stores

Why might performance decrease over time when performing exercise at a constant moderate intensity?

carb stores are depleted, switching metabolism over to fat oxidation, which is a slower and less efficient process and may result in decreased performance capabilities

What does the oxidative capacity of muscle depend on?

activity and number of enzymes such as succinate dehydrogenase and citrate synthase, fiber type composition, and oxygen availability and delivery

What is direct calorimetry?

a way to measure heat production in an insulated, airtight chamber to estimate energy expenditure

What are the limitations of direct calorimetry?

it is expensive, time consuming, technical, and cannot follow rapid changes in intensity

What is indirect calorimetry?

a method for measuring the respiratory exchange between O2 and CO2 as a measure of energy expenditure

What are the limitations of indirect calorimetry?

energy has to be completely oxidative without any help from anaerobic energy systems

What might measuring gas exchange during high intensity activity result in with regards to energy expenditure?

an underestimated energy expenditure

What variables do you need to know to perform indirect calorimetry?

VO2: volume of O2 consumed per min

VCO2: volume of CO2 produced per min

RQ (respiratory quotient) or RER (respiratory exchange ratio): VCO2 / VO2

What is measured by a metabolic cart?

Ve: volume of exhaled air

FeO2: fraction of O2 in exhaled air

FeCO2: fraction of CO2 in exhaled air

What is Dalton’s law?

that total pressure of a gas mixture is the sum of its partial pressures, meaning the fractional concentration of gas inhaled or exhaled is proportional to the total volume of a gas inhaled or exhaled

How would Dalton’s law be applied to VO2?

VeO2 = (Ve)(FeO2) and ViO2 = (Vi)(FiO2)

What is the standard fraction of O2 in normal room air?

0.2093 or 20.93%

What is the standard fraction of nitrogen in normal room air?

0.7904 or 79.04%

What is the standard fraction of CO2 in normal room air?

0.0003 or 0.03%

What is the Haldane transformation?

an equation used to calculate oxygen consumption by assuming that the volume of nitrogen inspired and expired is constant, meaning (Vi)(FiN2) = (Ve)(FeN2)

What does BTPS stand for?

Body Temperature at ambient Pressure is Saturated with water vapor

How does temperature, pressure, and saturation affect volumes of gas?

Warm temperature = increased volume

Increased pressure = decreased volume

Increased saturation = decreased volume

Why must BTPS or ATPS be standardized to STPD (standard temperature pressure dry)?

to allow for consistent comparisons across studies with varying temperatures, pressures, and saturations (humidity)

What is RER (respiratory exchange ratio)?

the approximate mix of catabolized energy, meaning RER = VCO2 produced / VO2 consumed

What is the RER for carbs?

1.00 because O2 in = CO2 out

What is the RER for fats?

~0.696 because O2 in > CO2 out

What is the RER of proteins, even if it is mostly ignored?

~0.818 because O2 in > CO2 out

What does a RER of 0.70 indicate? How many kcal/L of O2?

usage of 0% carbs and 100% fats

4.69 kcal/L of O2

What does RER of 1.00 indicate? How many kcal/L of O2?

usage of 100% carbs and 0% fats

5.05 kcal/L of O2

What does an RER of 0.85 indicate? How many kcal/L of O2?

usage of 50% carbs and 50% fats

4.85 kcal/L of O2

How can you calculate caloric equivalent?

by finding RER and relating it to energy expenditure (kcal/L of O2), then multiplying by the O2 we use and the time duration of the activity

What does calculating caloric equivalent ignore?

that we expend more calories beyond our work due to heat loss

What is the RQ (respiratory quotient)?

RER once other factors begin to impact metabolism

How can RER go above 1.00?

when exercise intensity increases, a higher proportion of carbs is used for energy production and as pH falls, the body’s buffering systems produce “nonmetabolic” CO2, raising RER

What are the limitations in regards to indirect calorimetry and RER?

it is only accurate at rest and during steady state

RER assumes oxidation is the only process going on

RER can actually go above 1.00 due to “nonmetabolic” CO2

RER ignores protein contributions

What is metabolic rate?

the rate of metabolism or energy expenditure based on VO2 and caloric equivalent

How can we calculate caloric expenditure (kcal/min)?

(VO2)(caloric equivalent)

Why does metabolic rate always increase proportionally within the first 1-2 min of exercise?

because aerobic energy systems are turning on, then reaching their steady-state

What is VO2 max?

the highest rate of O2 usage capable in the body, or maximal O2 uptake

What is the difference between VO2max and VO2peak?

subjects can reach volitional fatigue before actually reaching VO2max

How are we able to improve endurance if VO2 cannot continue to increase?

by improving our ability to perform at a higher percentage of our VO2max

Why is VO2max normalized to body mass?

because more weight traditionally means more work, which must be considered in FFM vs FM

What is lactate threshold?

the moment where lactate production exceeds lactate clearance

What does the lactate threshold indicate?

a switch to more anaerobic energy systems during exercise

Where is the lactate threshold in relation to VO2max in untrained and trained individuals?

untrained: 50-60%

trained: 70-80%

How can lactate clearance be improved?

improved oxidation: more MCT transporters, better blood flow through the muscle, and more aerobic enzymes

produce less lactate: training at higher intensities, more red blood cells and mitochondria, and improved O2 delivery

What does good endurance performance depend on?

a high VO2max, lactate threshold, percentage of Type I muscle fibers, and a economy of effort

What is the O2 deficit?

the difference in O2 needed versus O2 delivered, typically occurring at the beginning of exercise before reaching steady-state

What is excess post exercise oxygen consumption (EPOC)?

the period where anaerobic energy stores are being refilled, lactate is being cleared, VO2 consumed is still higher than baseline after exercising, and body temperature is high